It is well-known that titanium tetrachloride reacts with oxygen in the vapour phase to form titanium dioxide and that this reaction is initiated by heating the reactants to a suitable temperature. However hot titanium tetrachloride is highly corrosive and therefore many useful materials of construction for heat exchangers used to heat titanium tetrachloride are rapidly corroded. In practice this generally imposes an upper limit of about 400.degree. C. on the temperature to which titanium tetrachloride can be heated by conventional heat exchangers.
A suitable temperature for the reactants (oxygen and titanium tetrachloride) is about 900.degree. C. and, in order to achieve this temperature in known processes, the oxygen feed must be heated sufficiently to compensate for the above-mentioned relatively low titanium tetrachloride temperature. Frequently this high temperature for the oxygen feed is achieved by adding a fuel such as toluene to the oxygen as it is introduced into the oxidation reactor or by heating with an electrical discharge. However, the use of these methods of heating introduces unwanted impurities such as, for example, carbonaceous residues from the fuel or metallic impurities from the electrodes used for the electrical discharge.
Furthermore, the oxidation of titanium tetrachloride is exothermic and therefore higher temperatures than are desirable can result in the reactor, leading to a waste of energy.